1. Field of the Invention
The invention relates to a process for preparing silicone resins bearing hydroxy groups and alkoxy groups without addition of organic solvents.
2. Description of the Related Art
Silicone resins and precursors thereof can, as described, for example, in EP0927734, be prepared from chlorosilanes by partial or complete alkoxylation and subsequent partial or virtually complete hydrolysis in the presence of a solvent which is not miscible with water. The catalyst is usually the hydrogen chloride introduced by the chlorosilanes, or aqueous hydrochloric acid.
In the reaction of chlorosilanes with alcohol and water, it is an objective to recover the hydrogen chloride formed as completely as possible in order to avoid or minimize wastewater and reuse the hydrogen chloride for the chlorosilane synthesis. This occurs very successfully, as shown in DE102005003899, when using columns which consist of a reaction unit and a distillation unit. However, here too, the use of an organic solvent which does not participate in the reaction is necessary. Undesirable traces of this solvent, e.g. toluene, are frequently still present in the resin solutions and thus lead to restrictions to various fields of application.
The alkoxysilanes prepared from chlorosilanes by hydrolysis sometimes contain considerable amounts of chlorinated hydrocarbons due to the chlorosilane synthesis. Methods of chloride reduction with regard to such compounds by neutralization or removal by distillation are known. DE10332622 describes a process for dissociating chlorinated hydrocarbons which are present in alkoxysilanes and interfere in the further processing of alkoxysilanes as a result of hydrogen chloride formation. This process is complicated and the costs for the product are correspondingly high.